This invention relates to an improvement on an overlock sewing machine, and more particularly to an overlock sewing machine which pays out or feeds threads for various stitch shapes in association with the conversion of stitches, such as an overedge stitch, a double chain stitch and the like.
Japanese Laid-Open Utility Model Application Sho 61-31082 describes an overlock sewing machine for producing the various aforementioned stitch formations. The described overlock sewing machine adjusts the amount of feed thread by changing the position of a thread guide, which is so arranged to cooperate with a conversion from, for instance, the overedge stitch to the double chain stitch. Feed thread adjustment by an eccentric cam is described in Japanese Laid-Open Patent Application Sho 61-181488.
The above prior art references, however, include disadvantages in that the sewing machines do not accommodate the various stitch formations. More specifically, it is difficult to adjust the amount of feed thread to obtain the desired stitch formation since the aforementioned conventional sewing machines using the aforementioned thread guide and eccentric cam are not capable of varying the amount of feed thread, that is, whereas a large amount of feed threads is required for overedge stitching, a small amount of feed threads is required for roll hem stitching. In the aforementioned two publications, the amount of feed threads is not suitably adjustable by the described thread guide or eccentric cam.